1. Technical Field
The present invention generally relates to a semiconductor device manufacturing apparatus. More particularly, the present invention relates to a system used to determine proper alignment of a wafer loaded into an ion implantation device.
A claim of priority is made to Korean Patent Application No. 2004-50175, filed Jun. 30, 2004, the disclosure of which is hereby incorporated herein by reference in its entirety.
2. Discussion of Related Art
Generally, to manufacture a semiconductor device, various unit processes are performed on a semiconductor wafer. Among such unit processes is an ion implantation process, which implants impurities into a semiconductor wafer to change electric characteristics of the semiconductor wafer.
The ion implantation process is a process of implanting a P type impurity such as boron, aluminum, and indium, or implanting an N type impurity such as antimony, phosphor, and arsenic into a semiconductor crystalline structure in order to obtain desired conductive and resistive elements.
Such an ion implantation process can adjust an impurity concentration in a semiconductor wafer to a range of 10E14˜10E18 atoms/cm3. It is also easier to adjust the impurity and depth concentration with the ion implantation process than a diffusion process. Furthermore, since the ion implantation process can restrictively implant ions into local regions, the ion implantation process has a wider use. U.S. Pat. No. 5,475,618, for example, discloses an ion implantation device to perform the aforementioned ion implantation process.
FIG. 1 is a perspective view of a conventional ion implantation apparatus.
As shown in FIG. 1, the conventional ion implantation device includes an ion implanter 10 and a wafer loading mechanism 30. Wafer loading mechanism 30 positions a wafer, and ion implanter 10 implants impurity ions into the wafer.
Wafer loading mechanism 30 includes a loading station 32, an unloading station 33, and a process chamber 31. Loading station 32 and unloading station 33 respectively loads and unloads the wafer for an ion implantation process. After the wafer is loaded into a predetermined position in process chamber 31, ion implantation is performed under vacuum pressure or atmospheric pressure.
The wafer in process chamber 31 must be aligned in a specific direction, so that impurity ions can be implanted into the wafer at a precise angle by ion implanter 10. Accordingly, an apparatus to align and load the wafer in process chamber 31 is required. The aligned and loaded wafer is transferred to the ion implantation apparatus by means of a robot arm.
FIG. 2 is a perspective view of a conventional wafer alignment apparatus.
As shown in FIG. 2, the conventional wafer alignment apparatus includes a body 100, an alignment chuck 110, a guide plate 120, a plurality of sensors 130, and a wafer carrier cassette 150. Body 100 includes drivers such as a motor 102 and a pulley 104. Alignment chuck 110 protrudes at an upper center portion of body 100 to rotate a wafer. Guide plate 120 moves in a vertical direction to accurately locate a center of the wafer. In other words, after a wafer is positioned on alignment chuck 110, guide plate 120, which circumferentially surrounds alignment chuck 110, then moves up to properly seat the wafer in guide plate 120. The plurality of sensors 130 detect a flat zone of the wafer. Wafer carrier cassette 150 is supported by a plurality of frames 140 formed at respective corners of body 100. The wafer aligned by the plurality of sensors 130 and alignment chuck 110 is loaded onto wafer carrier cassette 150 in a specific direction. Although not shown, the conventional wafer alignment apparatus further includes a control section to control the drivers using a signal detected by the plurality of sensors 130.
Alignment chuck 110, guide plate 120, and the plurality of sensors 130 are disposed between body 100 and wafer carrier cassette 150. Alignment chuck 110, guide plate 120, and the plurality of sensors 130 are exposed to the outside.
Moreover, when a wafer is loaded by means of a robot arm, alignment chuck 110 adsorbs the wafer by suction and rotates it. At this time, alignment chuck 110 cannot move vertically.
Guide plate 120 moves vertically between alignment chuck 110 and body 100 when a wafer is loaded and unloaded from alignment chuck 110. However, guide plate 120 does not rotate.
Each of the plurality of sensors 130 includes a light emitting section to emit light, and a light receiving section to receive the light reflected by a wafer. The plurality of sensors 130 are fixed and located between alignment chuck 110 and guide plate 120. Preferably, a first sensor 130a and a second sensor 130b are formed to face each other centered about alignment chuck 110. When the wafer is loaded and rotated on alignment chuck 110, sensors 130a and 130b detect a flat zone at a side of the wafer's edge, which assists to align the wafer to a set location.
That is, alignment chuck 110 rotates a wafer in a first direction when first sensor 130a detects a flat zone of the wafer. Alignment chuck 110 stops the rotation when a second sensor 130b detects the flat zone of the wafer. Then alignment chuck 110 rotates the wafer in a second direction and stops the rotation when first sensor 130a again detects the flat zone of the wafer. By this method, the wafer is accurately arranged on alignment chuck 110 in either one of a predetermined programmed A mode or B mode.
However, if second sensor 130b fails to detect the flat zone of the wafer due to an interference from light from a source other than the light emitting section, alignment chuck 110 rotates the wafer by 360 degrees until first sensor 130a again senses the flat zone of the wafer. Accordingly, the wafer is inaccurately arranged on alignment chuck 110, and thus inaccurately loaded into an ion implantation apparatus.
Wafer carrier cassette 150 is a location to which the wafer aligned by alignment chuck 110 is moved by a robot arm to be temporarily stored. A plurality of wafers may be loaded onto wafer carrier cassette 150. The wafers loaded onto wafer carrier cassette 150 are moved to another wafer carrier cassette to be moved to a wafer loading station of an ion implantation apparatus.
Therefore, the conventional wafer alignment apparatus aligns the flat zone of the wafer using the plurality of sensors 130 and alignment chuck 110, and supplies the aligned wafer to ion implantation device by a robot arm.
However, as described above, the conventional wafer alignment apparatus has the following problems.
In the conventional wafer alignment apparatus, when external light emits sensor 130, sensor 130 cannot accurately detect the flat zone of the wafer.
Therefore, it would be desirable to provide an apparatus for aligning a wafer, which normally detects a flat zone of the wafer by sensors.